Rats can shake their heads rhythmically

Humans aren’t the only animals known to move to a musical beat.

For example, parrots do it too. And now rats have been observed shaking his head to the beat of the music of Mozart, Lady Gaga, Queen and others, researchers report Nov. 11 in Scientists progress.

Moreover, animals seem to respond to the same rhythms that cause humans to tap their feet. The study could help reveal the evolutionary underpinnings of the sense of rhythm in humans.

“Some of us believe that music is very special to human culture. But I believe that its origin is somehow inherited from our ancestors,” says Hirokazu Takahashi, a mechanical engineer at the University of Tokyo, who studies brain function.

The ability to recognize the rhythm of a song and synchronize one’s body movements to it is known as rhythm synchronization. It’s a mystery why some species, like humans and parrotshave the innate ability and others do not (SN: 04/30/09).

For the lab rats, Takahashi and his colleagues staged Mozart’s “Sonata for Two Pianos in D Major” (K. 448). The team sped up and slowed down the tempo, as well as played at its normal speed, observing the rats’ movements not only visually, but also with wireless accelerometers, which were surgically placed on the rats.

The team initially thought that body size could determine the tempos that triggered headbutts. Humans tend to prefer foot tapping to music that’s between 120 and 140 beats per minute, but a small animal like a rat would likely need a faster tempo to get the same reaction, emitted the researchers’ hypothesis.

“There are many reasons to think that maybe [rats] would prefer faster beats. But that’s not what they found. And it’s intriguing,” says Aniruddh Patel, a psychologist at Tufts University in Medford, Mass., who was not involved in this research. He studies musical cognition, the mental processes involved in the perception and response to music.

In the video recordings, the rats’ head bobbing was more pronounced when the sonata was playing at its usual rate, around 132 beats per minute. The same was true for 20 people who listened with headphones with accelerometers.

For humans and rats, headbutts were consistent at around 120 to 140 bpm. When the music was played faster or slower, there was no head bang. This suggests there’s something fundamental to the way the animal brain is tuned or wired to respond to rhythm, Takahashi says.

The team also played some of their favorite rat pop songs, including Lady Gaga’s “Born This Way” and Michael Jackson’s “Beat It,” and saw a similar response.

The researchers used motion capture cameras to track how the rats move to a musical beat. The colored dots indicate markers that helped cameras track the rodent’s subtle movements as it hears different pieces of music, including a Mozart piano sonata and Lady Gaga’s “Born This Way.”

While Patel agrees that rats seem to prefer rhythms that humans like, he isn’t convinced that rats can sync to rhythm the way humans do.

“I think this study actually raises more questions than answers in a way,” says Patel. Humans and parrots show beat synchronicity through large voluntary movements like head-nodding, dancing, or foot-tapping. The rats displayed very small movements that had to be captured with special devices like a head-mounted accelerometer and motion-capture technology.

The behavior was also more observable when the researchers enticed the rats to stand on their hind legs with their water bottle up high, rather than on all fours.

“The fundamental nature of beat perception and timing is that you predict the timing of the beat and move in a predictable way,” he says. “So we land just on pace or a bit ahead.” Since rats’ movements are so tiny, it’s unclear whether rats can predict beats or just react to them.

Both Takahashi and Patel point out that this study does not not show that rats like to dance to human music. “The musical stimulus is very appealing to the brain,” says Takahashi. But that’s not proof [that] they appreciate or they perceive the music.

Next, Takahashi seeks to see what other aspects of music we might share with rodents and other animals. “I might like to reveal how other properties, like melody and harmony, are also related to brain dynamics.”

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